Ultra high frequency power measuring system



lNvs-:NToR ugf I4( Jerome.

ATTORNEY R. w. GeoRef-i ULTRA HIGH FQUENCY POWER MEASURING SYSTEM 4Patented-Jan. 4, 1849 I ULTRA HIGH FREQUENCY POWER' HEASUBING SYSTEM nupnmccaammmamnammorto oorporati nadiocorpcrationofma 'Delaware ono! mutation Minh u, 1m, Serial No. 480,612

The present invention relates to an ultra high frequency measuring system for use at frequencies on the order of 3,000 megacycles or so.

9 Chinn.' (CL 17h-9B) one object or the invention is to provide an emcient microwave signal generator for use at ultra high frequencies in the range between 2000 and 4000 megacycles.

Another object is to provide a novel electron discharge device oscillator system having an adinstable coaxial line resonator connected between the grid and cathode of the device, and an adjustable low loss cavity resonator coupled between the anode and grid of the device.

A further object is to provide in an ultra high frequency measuring system, a stable reference level indicator utilizing a Wollaston wire.

A still further object is to provide an improved form of ultra high frequency voltage or current indicator utilizing a Wollaston wire connected in a bridge circuit which can beused at frequencies up to or above several thousand megacycles.

Various features of the invention relate to the arrangement which includes suitable mechanical drive ratios moving the cathode slider at a different rate than thegrid-anode cavity slider, and to the means for reducing the tendency for spurious oscillations to occur in the cavity resonator.

The single figure of the drawing illustrates the improved type of signal generator of the invention,l which utilizes, among other things, a novel form of oscillator and Wollaston wire and bridge circuit to indicate the signal' input level as a calibrating reference.

Referring to the drawing, the improved signal generator comprises a vacuum tube triode I, having associated with its grid G and cathode C a tunable coaxial line resonator circuit 2, l and associated with its grid G and anode P a relatively high Q `tunable resonant cavity 4. The vacuum tube I which is illustrated is 'of the type generally referred to as a lighthouse tube, and is described in more. detail hereinafter. The heating current for the cathode and the positive polarizing potential for the anode are supplied through high loss coaxial radio frequency low pass filter lines and 6, respectively.

Attenuatm The voltage or current indicator and associated bridge circuit II is incorporated with an attenuator cylinder III. The input end of the attenuator cylinder I0 projects into the interiorof the cavity resonator 4 (as shown) and carries a Wollaston wire in the form of van extremely thinwireofthiskindhasadirectcurrentresistance' which is the same as its resistance at the operating radio frequency for any fixed operating temperature. The direct current and radio frequency resistances of this wire are the same for a given power input only up to such high frequencies that the current distribution in the wire remains substantially uniform. Within the attenuator cylinder I0 there is provided a couplingfloop Il which is carried on and movable with a supporting cylinder Il. The end of the attenuator cylinder I0 which supports the Wol laston wire I2 is inserted within the cavity 4 for energizing the Wollaston wire. If desired, a suitable adjustment of the degree of coupling may be provided between the cavity resonator l and the cylinder I0. It should be noted that one end of the Wollaston wire I2 is directly connected to one end of the cylinder I0 while the other end of the wire I2 is capacitatively coupled to the cylinder I 0 by means of a small metallic plate` I! which is mounted upon but separated from the cylinder I0 by means of mica insulators. The

plate I5 is located at the end of the cylinder I0 which is slightly recessed to permit the plate I5 to be mounted on the cylinder without unduly projecting therefrom.

The movable cylinder Il in the interior of the attenuator pipe I0 and which carries the coupllng loop Il is movable in the direction of the length of the pipe I0 so as to adjust the position of the loop I3 toward or away from the resistance I2. Adjustment of the position of theloop I3 serves to provide different degrees of coupling to the field at the mouth of the attenuator cylinder I0. The output end of the attenuator system is connected totcable I6 which, if desired, may be connected by means of a jack to the attenuator and have such a loss' as to furnish a substantially fixed source of impedance, looking from the load, to which the cable I6 is connected, into the signal generator. That end of the Wollaston wire I2 which is capacitively coupled at I5 to the attenuator cylinder I0 is also connected by means of the high loss coaxial low pass radio frequency lter line I'I to the bridge circuit II In one particular embodiment of the invention, the attenuator cylinder I0 was rather small in diameter; namely, 0.200 inch, which, with an 5o associated suitable nut and thread arrangement involving an accurately cut forty threads per inch for the displacement control ofthe interiorly located support I4 and loop I3, provided an output change of the attenuator of four db. (decibels) thin 0.0001 inch platinum resistance wire I2. A 56 per turn of the control nut. The smalldiameter between actual and calculated rate of attenuation at low frequencies is on the order of one decibel in 200decibels. Attention'is directed to F18. 2 of my United States PatentNo. 2,204,179, granted June 11, 1940, for details of construction suitable for the nut and thread arrangement of the atten-'-` uator in order to provide an adjustment in posi'- tion of the coupling loop I3 relative tothe ope end of the attenuator cylinder Ill.

Bridge circuit i The bridge circuit I I, which is part ofthe cur rent or voltage indicatorsystem, includes a pair of fixed arms 1 and 8, an adjustabley arm Land the Wollaston `wire I2 constituting V the Vfourth* arm Wollaston wire I2is connected to the bridge I I` through the low pass radio frequency filter line Il. have a range of/ from zero to 200`microamperes, is connectedacross the'bridge between the junc- A` suitable meterMj which may.

the cavity resonator 4.

4i These metallic rings or discs make contactall around their respective electrodes and connect withthe cavity resonator 4 on opposite sides of 'the cavity, as shown.A One such light house tube, mentioned here byway of example, is the General Electric type GL-446 triode, which has been used''satisfactorilyV in severa1 embodiments of the invention. The oscillator vacuumtube is held in placevby spring pressure on the base, which forces the grid Vand plate lrings against theirv respective contact springs (not shown) in The grid-'cathode circuit includes a tunable coaxial line having'an inner cylinder 3 and an outer cylinder 2, connected together at one end by an end plate 2li; The inner conductor 3 of the l'coaxial line is large enough to accommodate in its interior thecathode of the tube and. its surenergy.

tion points of arms l and 8 and arms land I2. l

The Junctionpointkbetween the ixed arm ,8 and the cable I'I is grounded y(as's'hown), while the junction point between the'ilxed arm 'I and the adjustable arm includinglresistors is connected to a regulated power supply I8 through a resistor I9. 'I'his power supply, by way of example,may supply i150 volts to the resistor I9. This bridge circuit, it will be seen, is substantially identical with the' bridge circuits f Figs. 3 and 4 of my copending Unitedv States application vSerial No. 408,570, filed August 28, 1941, now U. S. patent 2,399,481 to which reference is made, and wherein a Wollaston wire is used having a resistance of about 73 ohms.

In order to .measure the. current or voltage, the bridge .I I is first balanced with no radio frequency voltage applied.' to the Wollaston wire I2. vThe application of radio frequency voltage to the Wollastonvwirei I2 caused by exciting the cavity resonator 4 will cause the Wollaston wire to' heat up and its resistance to increase, thus throwing the bridge out of balance and producing a deflection on the microammeter M. The sensitivity of the bridge circuit is determined in part by the resistance I9 in series with the regulated power supply vequipment I8. The deflection on the microammeter M, it will be understood, is merely anivindication of the lrelative magnitude of the poiivfrlinl the Wollaston wire I2. If desired, in order to. usethe bridge as a volt or current meter, it is necessary to'v calibrate the deflection of the microammeter for known amounts of power vmeasured at lowfrequencies in the Wollaston wire I2. This can be done by utilizing a suitable known voltage calibrating source to replace the radio frequency voltage in order to provide the same power in Wollaston wire l2 to give the same deflection. I'he bridge circuit can thus be used either as a volt or a current meter (or power).

` Actually, all `that is required is a stable reference level indicator.

l y Oscillator The oscillator circuit includes a vacuum vtube I of they flight house type, wherein the grid and anode' connections protrude through the glass envelope in the form of metallic rings spaced from one another along thelength of the tube.

4of the resonator I to the anode ring.

rounding envelope, as shown. 'I'he end plate 2li is provided with'an aperture 2l in its center,

to permit a connection from the heater of the cathode to kextend through the high loss Acoaxial radio frequency filter line I to a source of heater Ihe tunable coaxial line. 2, 3 is adjustable by means of a slider 22, which extends entirely around the inner conductor 3 and has contact springs connectingxboth the inner and outer conductors of the coaxial line resonator. This slider 22 has a multiplicity of contact springs making contact with the inner and outer conductor all around the interior of the resona-y tor, and is provided with a plurality of plunger rods 23, 23, in turn, connected together and to a control knob 24.

The cavity resonator 4 is directly connected on one side (the upper side shown in the drawing) to the grid ring, so that this side of the resonator makes contact lsubstantially all around the grid ring. This cavity resonator is coupled on its opposite side (the lower side shown in the drawing) to the anode ring from which itis separated only -b'y a thin mica ring (not shown); forming a radio frequency by-pass capacity which has an extremely low impedance tothe radio frequency energy of the operating frequency. This capacity is represented diagrammaticallyby the dotted capacitors 3l which connect the lower side Thus, opposite sides of the cavity resonator are coupled to the grid and anode rings of lthe light house" vacuum tube I. The cavity length is controlled by means of sliders 25, 25 symmetrically disposed on opposite sides of the tube I, it being understood that the tube I is located along one axis of the resonator.

It is preferred that the electrical length of the cavity be one wavelength at the operating frequency so that the vacuum tube I is located at a relatively low impedance point in the plate-grid tuned circuit. the desired mode of oscillation in the cavity resonator 4 is primarily obtained by suitable tuning of the cathode-grid coaxial line resonator 2, 3. However, with certain cathode tuning'adjustments, the feed-back may be found suitable to` support more than one mode of oscillation, with the result that undesired frequencies will be ob tained.- Avoidance of these undesired frequencies which may be present at one time is usually achieved by changing the length of the' cathode-grid tuning circuit by amounts equal to one or more multiples of a half wavelength, thereby retaining proper feed-backphase relations for the desired frequency -while substantially altering the feed-back yrelations for the undesired frequency.

4Sliders 2l, 2l oi' the cavity resonator 4 are both linkedtogether and, in turn, connected through fatraedierent rate than the sliders 25, 25 of the dgrid-anode cavity 4. It is preferred that there be provided a secondary 'adjustment control (trimmer) of the cathode-grid circuit in order to-obtain the most efficient oscillation condition. This secondary adjustment control which is connected only to the plunger rods 23, 2 3 may be operated by pushing a knob in the panel /to disengage the locking mechanism connecting the knob 24 with the gear box 28, and turning it either to the right or the left. as desired.

In one embodiment of the present invention satisfactorily constructed and operated, the oscillator was designed to operate at frequencies between 2700 megacycles and 3700 megacycles. A spurious lower frequency oscillation mode, occurring near a desired frequency of about 2825 .megacycles was substantially suppressed by the use of a small short circuiting element 20 inserted between the walls of the cavity 4 near the tube I and across the narrow dimension oi' the cavity. An apparent eii'ect of this suppressor 30 is to reduce the frequency versus change in cavity length in the region of thefrequency at which the spurious oscillation was had. A tendency of the oscillator to jump to a higher frequency mode was found when the anode input voltage was raised above a critical value at the lower frequencies, around 2700 to 2800 megacycles, corresponding to a wavelength of approximately ll centimeters. Satisfactory operation was had in this particular case by using a minimum required anode input voltage. The existence of this spurious mode was indicated by an abrupt increase in oscillation intensity.

In an embodiment of the invention tried out in practice, the oscillator functioned easily to provide anormal output at 3000 megacycles with an anode current of millianiperesv and an anode voltage of 220 volts. In another embodiment, a power output of seven tenths of a watt was obtained at 2700 megacycles with qve watts anode power input.

The use of the high loss coaxial lines 5 and l, serving as radio frequency illters, substantially eliminate radio frequency leakage. The high loss in these lines was obtained by drawing copper tubing over a varnish impregnated cotton covered iron wire. Each ilter line in one embodiment of the invention was about ten feet long and wound on a spool for compactness.

If desired, the narrow dimension part of the grid-anode cavity 4 on the side opposite that in which the attenuator is inserted, may be provided with a tapped hole in. which a coupling loop can be inserted and power taken out for general purposes.

What is claimed is:

1. The combination with an ultra highA frequency generator including a radioy frequency oscillator tunable over a band of frequencies, a

hollow body resonator for determining the fre-v resonator, said attenuator having a Wollaston wire coupled across said one end of said pipe,

said wire being in coupling relation with theI .radio frequency magnetic field in said resonator, -and a resistance change indicator circuit coupled to said Wollaston wire..

. 2. The combination with an` ultra high frequency oscillator which is tunable over a band oi' frequencies and has a hollow bodyresonator as a frequency determining element, of a resistance change indicating bridge circuit having as one* arm thereof a Wollaston wire in coupling relation to the radio frequency field within said resonator, said Wollaston wire ybeing connected to the elements of said bridge through a high and a resistance change indicator coupled to said losscoaxial line low pass radio frequency filter.

3. The combination with a hollow body resonator having means for producing a radio frequency `magnetic field therein. of means for determining the reference level of said field, said means comprising an attenuator having a hollow .metallic pipe, one end of which is inserted into said resonator body. a Wollaston wire coupled across said one end `of said pipe, and a resistance change indicator coupledv to and responsive to changes in resistance of said Wollaston. wire.

4. The combination with a hollow body resonator having means for producing a ratio frequency lmagnetic field therein, of means for determining the reference level of said field, said means comprising an attenuatorl having a hollow metallic pipe, one end of which is inserted into said resonator body, and a Wollaston wire coupled across said one end of said pipe. a coupling loop within said pipe near said Wollaston wire, means for moving said loop toward or away from said Wollaston wire. a load coupled to said loop, and a resistance change indicator coupled to said Wollaston wire.

5. In combination, means for producing a magnetic field, and means for determining the reference level of said field, said last means including a hollow metallic pipe having one end located in vsaid field, and a Wollaston wire one terminal of which is directly connected to said one end of said pipe and the other terminal of which is capacitively coupled to said one end of said pipe,

Wollaston wire.

6. In combination, means for producing a magnetic field, and means for determining the reference level of said field, said last means including a hollow metallic .pipe having one end located in said field, and a Wollaston wire .one terminal of which is directly connected to said one end of said pipe and the other terminal of which is responsive to changes in. temperature of said l wire, and an adjustable output coupling loop within said attenuator pipe.

l8. An attenuator circuit for determining the reference level of a radio frequency magnetic field, 'comprising a hollow pipe having a Wollaston wire of a thickness of the order of .0001 inch coupled across one end of said pipe and in coupling relation to said field, a coupling loop tile.of this patent:

e Y 7 I located within and adlustablcin position along.

said pipe, said loop bein: located near said Wollaston wire, and an. output circuit coupled to said loop.

9. Means for measuring the signal level input` to an attennator pipe, including a iine platinum resistance wire of theorder oi' 0.0001 inch thick mounted across the input end ci said attenuator' Y ,Y nnranancss orrm The following references are oi record in the aumen? UNITED STATES PATENTS Y Number Name Date 787,971 Stone Aug. 18, 1 904 1,901,741 Fetseh Mar. 14, 1933 2,104,918 /Evans `Jan.,11, 1938 2,106,713V Bowen Feb. 1, 1938 2,125,969 Turner -..'Aug. 9,'1938 2,151,118 King et al. Mar.'21, 1939 2,232,179 King Feb. 18, 1941 2,238,298 Weholin Apr. 15, 1941 2,278,887 e Brown Apr. 7, 1942 2,284,879 Dow May 28, 1942 2,385,207 Moles ---.1 Dec. 19, 1944 2,399,481 y George Apr. 30, 1946 2,400,777

zo pages 228, 238, and 237. Copy in Division 51.

om --.my 21, 194s. 

